1 1.a What was the purpose of incubating the uninoculated plates? Be specific. To be used as a negative control, nothing should grow on these plates. 1.b What is an appropriate name for these plates? Control group. 1.c If growth appears on both uninoculated plates, what are some likely explanations? If growth appears on one plate it most likely occurred from contamination, or when the media was made. 1.d What if growth appears on only one plate? If growth only on one plate it most likely was contaminated while making or using the plate 1.e . How does growth on the uninoculated plates affect your interpretation of the other plates? Growth of the uninoculated plates means that there was either an error, contamination , or their before and makes the other plates suspicious. Both plates then probably need to be redone. 2 Why do you think the specific types of exposure (air, hair, tabletop, etc.) were chosen for this exercise? They were chosen because they are major sources of environmental contaminations. 3 3.a Did you get different-appearing colonies on plates 2 and 3? If so, explain why Yes because of more growth at a higher temperature. 3.b What is the likely source (reservoir) of organisms that grew best at 35°C, and how do they survive at room temperature without nutrients? Microbes grow better in 35 C due to it being close to human’s temperature. Microbes survive at room temperature by becoming inert and nutrients present, but not visible. 4 Suppose plate 4 (cough) has no growth after incubation. It is highly unlikely the “cougher” has sterile coughs! Suggest reasons why no growth was recovered on the plate One or more necessary resources for airborne microbes required for growth are not included in the nutrient agar media 5 The plates you are using for this lab will be autoclaved to completely sterilize them. The measures taken to disinfect the tabletops (the source of the organisms on plates 2 and 3) are not as extreme. Why The platves should have a higher cell density then the growth on the table , therefore the plate presents a greater threat then the countertop. 2.3 Organism Description and sketch Micrococus luteus Coloration around the slant and about 3 spots Rhodospirllum rubrum Lots of growth, spread out fans and lines Bacillus subtilis Little growth, few small spots 1. Match 1. Produces colored growth-Pigmented 2.Smooth texture with solid edge-Filiform 3.Solid growth seeming to radiate outward- Spreading edge 4.Almost invisible, or easy to see light through- Transparent 5.Rough texture with crusty appearance-Friable 2.List some reasons why growth characteristics are more useful on agar plates than on agar slants. 3.Why are agar slants better suited than agar plates to maintain stock cultures? (Think in practical terms, not necessarily in biological terms.) Agar slants are better suited than plates because they can be capped to prevent the agar and culture from drying out. The cap also prevents airborne contaminants from entering the slant. 4 Suggest possible reasons for how temperature affects pigment production (as in Fig. 2.33) Some chemical reactions are affected more by temperature than others 2.4 1. Organism Description Control No growth Crocossus luteus A little bit of growth Monas fluorus No growth Branhamella A Lot of growth, change in color to a light orange Providencia Officious No growth 1. Match 1. Evenly cloudy throughout-Uniform fine turbidity 2.Growth at top around the edge-Ring 3.Growth on the bottom-Sediment 4.Membrane at the top-Pellicle 5.Suspended chunks or pieces-flocculent 2.What factors besides physical growth characteristics of the organism are important when recording data about an organism? Why? Other important factors to include would be the growth medium, incubation temperature and atmosphere, some factors increase chance of cantomation or growth.